This is not a practical way of quoting boiler outputs, though manufacturers continue to specify the number of radiators. The output, and so the input, required from the boiler varies according to the size, from a small radiator in a toilet of about 300 Watts to a large one in a sitting room that is 3 kW, and so needs 10 times as much. If you already have a heating system that works you can look at the output of your existing boiler.
However, many were oversized in the past, and, no, there is no advantage in this – it just makes the boiler turn on and off frequently. If you want to check, you can get radiator output from manufacturers’ charts from the internet or from a plumbers’ merchant. These chart the output, which you can total up. A competent plumber / installer will also be able to help you size the house up; a lot will depend on your levels of insulation. To compare to other manufacturers they state 16 radiators for this size of boiler.